The present invention relates generally to cellular mobile communication systems. In particular, the present invention relates to a method and system for permitting seamless wireless telephone service across mobile switching centers that support multiple or different standards.
Cellular telephone service has been in widespread use for several years. Typical systems are characterized by radio coverage divided into small areas or xe2x80x9ccellsxe2x80x9d using low power transmitters and coverage-restricted receivers. Such systems are described in U.S. Pat. Nos. 3,906,166 and 4,268,722. A cellular system is typically characterized by a pair of radio frequencies associated with each radio channel in each cell. Several voice channels and at least one signaling channel (also known as a control or access channel) are associated with each cell. The signaling channel processes requests for service to and from mobile and portable phones in order to permit the mobile or portable phone user to converse with another party. A series of Mobile Switching Centers (MSC""s) associated with the cellular system provides the logical control features for efficient call routing and processing.
Numerous intersystem standards or protocols for U.S. cellular radiotelephone systems have been promulgated by the Electronics Industries Association/Telecommunications Industry Association (EIA/TIA) in order to ensure compatibility between MSC""s manufactured by different vendors for use in the United States and its territories. For example, United States manufacturers currently support the ANSI-41 standard in their MSC equipment. For various reasons, such standards have not been adopted globally. Rather, the cellular networks in many foreign countries are characterized by different protocols. For example, the European Community favors a standard known as A Global System for Mobile Communication (GSM). Other nations, such as South Korea, have adopted their own internal standards, for example, a standard referred to as K-MAP, for cellular communications networks. Such standards differ in the particular content and format of the messaging involved over the datalink connecting MSC""s in a cellular network.
In foreign countries, service providers are recognizing that superior technology and enhanced features sets are provided by MSC equipment manufactured in the U.S. and supporting standards such as ANSI-41. Unfortunately, for such foreign service providers who have implemented their networks according to different standards or protocols, adoption of the new standards is problematic and expensive. Because simultaneous replacement of the entire network of MSC equipment is prohibitively costly, such service providers have opted to migrate gradually to the new standards. During this transition, it is advantageous and necessary to provide MSC""s which are capable of supporting both the old and new standards. However, a system for providing seamless service between an MSC supporting only the old standard to an MSC supporting the new standard has not heretofore been provided.
The aforementioned problems can be further illustrated with reference to a cellular system according to the prior art Korean K-MAP protocol. The messaging and call routing according to such a system is illustrated in FIG. 1. As will be recognized by those of ordinary skill, the thin profile arrows in FIG. 1, and the subsequent FIGURES, represent messaging via the signaling channel and datalinks connecting the MSC""s. The broader profile arrows depict voice channel communication that is routed over the trunk lines (not shown). Consistent with the same convention, a capital letter designation for message names represents an inquiry or invoke message, while lower case letters represent return results.
The term INCALL is used throughout this specification to refer to an incoming call which may arrive from the Public Switched Telephone Network (PSTN) or from another mobile phone. The term xe2x80x9cV-MSCxe2x80x9d will be used throughout this specification to refer to a Visited MSCxe2x80x94an MSC associated with the particular cell visited by the mobile. The term xe2x80x9cH-MSCxe2x80x9d will be used throughout this specification to refer to a Home MSCxe2x80x94an MSC where the subscriber record for the mobile resides. The term xe2x80x9cO-MSCxe2x80x9d will be used to refer to the Originating MSCxe2x80x94the MSC where the call to a mobile originates.
Referring to FIG. 1, when mobile 10 is powered-up or enters a cell, the mobile registers in that particular cell. When mobile 10 registers, the V-MSC sends a message, REGISTRATION(MSRN) to the H-MSC. REGISTRATION(MSRN) includes the Mobile Switch Routing Number (MSRN) which identifies the V-MSC. The MSRN is stored at the H-MSC for future reference. An MSRN is a static 14-digit number defined by the K-MAP standard that identifies a particular MSC and enables any other MSC in the system to address the MSC via datalink. In an MSRN, the first 7 digits identify the visited MSC and the last 7 digits identify the mobile unit. In response to the REGISTRATION(MSRN) message, the H-MSC returns a registration profile in the message registration(profile) which contains information about the particular services available to the mobile subscriber.
In accordance with prior art systems, both the O-MSC and V-MSC communicate with the H-MSC using the same protocol, for example, K-MAP protocol. When an INCALL arrives at the O-MSC, a K-MAP message, Routing Information Inquiry (MIN) (RII(MIN)) is transmitted to the H-MSC, requesting the Mobile Identification Number (MIN) of the mobile phone. In response, the H-MSC will return a K-MAP message, rii(msrn) including the MSRN of the V-MSC. Once the O-MSC has been provided with the MSRN of the V-MSC, the voice call is trunked from O-MSC to the V-MSC using the public network. The voice call is then transmitted via radio frequency from V-MSC to the mobile unit.
The aforementioned problems can be her illustrated by a hypothetical system where the V-MSC and O-MSC are connected to the H-MSC using different protocols, for example, where the O-MSC is an older unit adhering to the K-MAP protocol used in Korea and the V-MSC is a new unit adhering to the ANSI-41 protocol. The H-MSC is equipped to communicate in multiple protocols. However, under the K-MAP protocol, when an INCALL arrives at the O-MSC, the message RII(MIN), is sent to the H-MSC and the O-MSC xe2x80x9cexpectsxe2x80x9d a return response in the format of the message rii(msrn) containing the 14-digit MSRN of the V-MSC. However, the ANSI-41 protocol does not support a 14 digit static number such as the MSRN. Instead, ANSI-41 provides dynamic numbers associated with particular mobile calls. These numbers are known as Temporary Local Directory Numbers (TLDN""s). As a result, the O-MSC adhering to the K-MAP standard would not xe2x80x9cunderstandxe2x80x9d a return result of a TLDN from an H-MSC operating under ANSI-41. Thus, the INCALL cannot be delivered to the mobile.
State-of-the-art MSC""s support multiple protocols and may converse individually with neighboring MSC""s in different standards. These MSC""s permit the service provider to specify a given standard, i.e., K-MAP or ANSI-41 when provisioning datalinks between the state-of-the art MSC and other MSC""s in the network that communicate according to only a single protocol. A state-of-the-art MSC is capable of routing a call from one K-MAP MSC to another K-MAP MSC or from one ANSI-41 MSC to another ANSI-41 MSC. That is, during any given time, they are able to xe2x80x9cspeakxe2x80x9d either K-MAP or ANSI-41, but not both, while processing a particular call. Thus, state-of-the-art MSC""s are not capable of providing seamless service from a K-MAP MSC to an ANSI-41 MSC. It would therefore be desirable to provide a system, including a method and an apparatus which permits seamless service between MSC""s operating under different protocols.
The invention provides systems, including methods and apparatus, for providing seamless telephone service across MSC""s that support multiple or different protocols. In accordance with a preferred embodiment of the invention, the H-MSC, in response to a first inquiry signal from the O-MSC requesting the identity of the V-MSC, sends a first response signal identifying itself to the O-MSC. The first response signal identifies the H-MSC according to the first protocol, for example, by forwarding its own MSRN as defined by the K-MAP standard. In essence, the H-MSC xe2x80x9cfoolsxe2x80x9d the O-MSC into xe2x80x9cthinkingxe2x80x9d that the H-MSC is the V-MSC. The INCALL is then routed to the H-MSC. Once the INCALL is routed to the H-MSC, it can then be routed to the V-MSC via messaging in the second protocol on the datalink connecting the H-MSC and V-MSC. For example, the H-MSC sends a second inquiry signal to the V-MSC according to the second protocol by requesting a Temporary Local Directory Number (TLDN) as defined by the ANSI-41 standard. The second inquiry signal represents a request for an identification number identifying, in the second protocol, the V-MSC. In response to the second inquiry signal, the V-MSC returns a second response signal to the H-MSC. The call is then routed from the H-MSC to the V-MSC and sent to the mobile unit from the V-MSC via radio link. Thus, the INCALL is seamlessly routed from the O-MSC to the V-MSC.
In accordance with another preferred embodiment of the invention, in response to a first inquiry signal from the O-MSC, the H-MSC sends a second inquiry signal to the V-MSC. The first inquiry signal represents a request for an identification number identifying, in the O-MSC""s protocol, the V-MSC. The second inquiry signal represents a request for an identification number identifying, in the V-MSC""s protocol, the V-MSC. In response to the second inquiry signal, the V-MSC returns a first response signal to the home mobile switching center, identifying the V-MSC in the V-MSC""s protocol. In response to the first response signal, the H-MSC sends a second response signal to the O-MSC, the second response signal representing, in the O-MSC""s protocol, a number identifying the V-MSC. Once the O-MSC is provided with the identifier of the V-MSC, the call is directly routed from the O-MSC to the V-MSC.
A primary advantage of the present invention is that it provides a system for seamlessly providing mobile telephone service across mobile switching centers that adhere to different messaging protocols without requiring changes to the message processing features of those mobile switching centers. That is, neither the V-MSC nor the O-MSC requires any changes to their message processing control logic.
Other objects, advantages novel features, and the further scope of applicability of the present invention will be set forth in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.